In recent years, low fuel consumption of vehicles has been desired in terms of environmental problems and the like. Thus, it has been and is being studied to operate an internal combustion engine using gasoline as fuel (hereinafter, also referred to as a “gasoline engine”) at an air-fuel ratio leaner than a stoichiometric air-fuel ratio, i.e. in a state where an excess air ratio λ is larger than 1 (hereinafter, also referred to as “lean combustion”). For example, JP2010-196517A discloses a technique for diffusive self-ignition combustion of gasoline by forming a high temperature field in a cylinder (combustion chamber) by pre-combustion and injecting the gasoline to pass through the high temperature field. According to this technique, diffusive self-ignition combustion similar to that of a diesel engine is possible also in a gasoline engine, wherefore fuel consumption performance can be improved by performing lean combustion.